U.S. Pat. No. 5,094,596 discloses a pump having a pair of opposed and interconnected pistons reciprocable in respective cylinders to pump paint. The interconnected pistons are driven in their reciprocatory motion by an air motor and while one piston and cylinder arrangement is pumping paint to supply paint under pressure into a pressure loop, the other piston and cylinder arrangement is being re-charged by drawing paint from a reservoir into the cylinder for subsequent discharge therefrom into the pressure loop in a subsequent reverse movement of the pistons during which the first mentioned piston will draw paint into its respective cylinder to re-charge that cylinder.
Air motors require an external source of compressed air in order to operate, and it is recognised that such systems are relatively inefficient in terms of energy utilisation. Moreover the change in drive direction at each end of reciprocatory stroke of an air motor is relatively slow giving rise to noticeable pulsation in the output of the pump. U.S. Pat. No. 5,220,259 discloses a single reciprocating piston pump of relatively large stroke driven by a D.C. electric motor, an arrangement which is disadvantageous in requiring a complex, and therefore expensive control arrangement for the motor.
It is an object of the present invention to provide a twin opposed piston reciprocating pump which is driven electrically in a simple and convenient manner.